Multiplex telegraph system



July 6g l937 J. L. CALLAHAN 4 MULTIPLEX TELEGRAPH SYSTEM Filed Junev 28, 1934 3 Sheets-Sheet 1 ATTORNEY July 6, 1937. J, CALLAHAN 2,086,351

MULTIPLE); TELEGRAPH SYSTEM Fild June 28, 1954 sheets-sheet s J. L. CALLAHAN ATTORNEY Patented July e, t19e-1 UNITED STATES PATENT oFFlcE MULTIPLEX TELEGRAPH SYSTEM of Delaware Application June 28, 1934, Serial No. 732,768

s claims.

This invention relates to a multiplex telegraph communication system for relaying radio signals.

'I'he present invention contemplates the use of a multiplex system which operates on the time division principle whereby a predetermined length of code unit, in thefpresent case the dot length,

is regarded as the basic unit and the successive basic units of the signal characters of each channel are divided into equal portions of like number as the several channels. In this type of system the transmission circuit is assigned consec- `utively to successive channels for a time interval equivalent to one of these-*equal portions, the remaining portion of each basic unit of 'each channel being discarded and subsequently restored at the receiving unit of the circuit. In other words,

the transmission line time is arranged lto be divided equally among the different channels so that each channel has a period of transmission 0 time allotted to it which is equal at most to the longest period of which the duration of the individual signal units forming the code are exact vmultiples, so that each signal unit comprises an equal number of components.

For a more detailed description of the use of the time division principle in multiplex systems, reference is herein made to United States Patent No. 1,979,484, granted November 6, 1934, to IR. E. Mathes.

It is anobject or the .present invention to provide a signal relaying arrangement for a multiplex telegraph system wherein a trunk station may communicate with one or more distant branch receiving stations through a remote, automatically controlled, trunk station. By trunk station is meant an oillce which is provided with` equipment for transmitting and receiving time division multiplex signals of the type hereinabove described, and by branch station is meant an ofdce which is provided with equipment for receiving time division signals and, if desired, apparatus for transmitting only code full length signals.

A further object is to provide means which.

enables the remote trunk station to synchronize the rotating mechanism at a branch office receiving station with respect to speed and phase.`

'Ihe advantage of this particular .method of communication which discards portions of the signals and combines other portions from-a plu rality of channels is that it is extremely confusing to unauthorized listeners, thus resulting in a practical commercial` recy arrangement.

In general, the prest. invention comprises a time division multiplex radio telegraph system for relaying Morse code signals iromal trunk stationA to one or more distant branch oilice stations through the intermediary of a central remote trunk station. Assuming, for purposes of illustration, that a local trunk station is located at New York, a branch oilice station at Los Angeles and the remote trunk station at San Francisco, it is proposed to receive the signals transmitted from New York at the San Francisco trunk station and to store` them in any desired manner before retransmitting the signals to the Los Angeles branch office station. 0f course,'other receiving stations may be located along the coast to receive the same signals relayed by the remote trunk station. At the remote trunk station, the dier` ent message signals which are received over the Various trunk channels are each made to operate storage equipment in the form of reperforators which, in turn, feed 'tape into automatic tape transmitters, the latter controlling, through a distributor, a radio transmitter associated with the remote trunk station. 'I'he steep wave front of the signal characters is arranged to control the rotating mechanism at the distant branch ofcestations. Thus, the signals from New` York synchronize theequipment at the central station lat San Francisco, and the signals retransmitted from San Francisco synchronize the equipment at Los Angeles from a speed and phase standpoint. Any one of several known methods for accomplishing this sort of synchronization may be employed, although it is preferred to use one'of the systems described in detail in the copending applications of R. E. Mathes, Serial Nos. 645,171

and 708,378, filed December l, 1932, and January 26, 1934, respectively, patented April 21, 1936', No.

2,038,375, and Nov. 24, 1936, No. 2,062,009, re-

spectively.

At the local multiplex trunk station (in this case New York) in the relaying system, which for illustration will be called the transmitting trunk station, there are employed a plurality of automatic tape transmitters, one for each channel, which are under the control of a drive motor, the latter in turn being responsive to a constant speed motor control unit. A specially designed brush and commutator device associated with the shaft of the drive motor functions to control the speed of the automatic tape transmitters. A multiplex distributor is used to assign the multiplex equipment and its associated radio channel to the diiferent auto tape transmitters successively, whereby only portions. of the code signals of each channel are assigned and' transmitted and the remaining portions ofthe signals discarded.l

At the remote trunk station in San Francisco, the received signals are assigned by a distributor, whose rate of speed is synchronized by the'incoming signals, to a special arrangement for rebuilding the discarded portions of the basic time units of each channel so that the signals i are restored to their original form. The signals p motor whose shaft is employed to synchronize the speed of the automatic tape transmitters at the remote trunk stations in a manner similar to that employed at the local trunk transmitting station. A section of the multiple unit distributor at the remote trunk station at San Francisco is used to control channels outgoing to the distant (local) trunk station at New York, which channels may contain signals originating at the branch office' station at Los Angeles, the remote trunk station at San Francisco, or both.

The branch oilice station at Los Angeles, in brief, comprises a receiving circuit similar to that employed at the remote trunk station at San Francisco. This station has, in addition, an automatic tape transmitting arrangement for sending signals to the remote trunk station where they may be relayed back to the local trunk transmitting station at New York, if desired.

In the accompanying drawings, Fig. 1 illustrates a local trunk station, herein called the transmitting station, Fig. 2 a remote trunk central station for relaying the signals received from the transmitting station, and Fig. 3 a branch of- Atice station,-of the multiplex telegraph relaying system of the invention.

Referring to the transmitting station of Fig. 1 in more detail, hereinabove referred to as the New York local trunk station, there are shown three line channels I, 2 and 3 over which are transmitted regular Morse signal characters to the centrally located transmitting multiplex distributor equipment.

The machines for transmitting the signals are arranged at some distance fromthe multiplex distributor equipment and are connected thereto by land lines, herein indicated as 4, 5, and 6. The multiplex equipment of the transmitting station Vand the automatic tape transmitters may, if desired, be located in the same building, the latter in the customary installation being located at some distance from the actual radio antenna equipment, herein designated as 1, and connected thereto by a land line such as 8.

For transmitting the Morse signals over channels I, 2, and 3, there are shown automatic tape transmitters 9, I0 and II which are controlled by perforated tape, by well known means, not shown, the perforations in the tape being made in accordance with the desired signal characters. 'I'hese automatic transmitters are shown as of the Wheatstone type, although it will be obvious that, if desired, the Creed apparatus may be employed. The rate at which the signals are transmitted from Aeach of themachines 9, I0 and II is determined by the respective motors 3, I3, and I4, the latter, in turn, being under control of the multiplex equipment which functions to transmit, alternately,v positive and negative sneden pulses to the motor equipment over land line I2. A brush and commutator arrangement on the common distributor drive shaft I5 provides a control frequency for the automatic transmitters 8, I0 and I I which is held to a high order of accuracy by drive motor I6. Line I2, extending from the brush and commutator arrangement on the distributor shaft is in circuit with polar relays I'I, I8 and 20, which are respectively individual to the drive motors 3, I3 and I4 of the automatic tape transmitters 9, I0 and II. The contacts of these polar relays, in conjunction with commutator and brush combinations on the shafts of the respective motors 3, I3 and i4, which are similar in construction to that on the distributor shaft I5, act to hold the motors 3, I3 and I4 toa constant speed and phase by cutting resistance in and out of the respective elds and armatures of the motors, as shown. At the desired constant speed and phase the automatic transmitters 9, I0 and II will transmit the pulses to the multiplex distributor I9 at the proper predetermined intervals.

The brush and commutator arrangement shown associated with motors 3, I3, I4 and I6 merely comprises two' full length insulated segments a and b and two half length insulated segments d and e, all of which are insulated from each other, as shown in the drawings. One of the half segments e is connect'ed to a full length segment a and the other half segmentd is connected to a full length segment b in such manner that individual brushes associated with the fulll length segmented portions are alternately connected to each of the commutators d and e, consecutively as the drive shaft revolves. In this manner, positive and negative pulses are transmitted from the multiplex driving unit over line I2 to the polar relays I'I, I8 and 20, causing these relays to vibrate and, in turn, to v apply positive and negative pulses to their respective commutator and brush assembly units for controlling the speed and phase of the drive motor units 3, I3 and I4. 'I'his method of control is well known in the art and functions in a manner which is obvious from a mere inspection of the drawings. A somewhat similar method of motor control is described in United States Patent No. 1,829,420, granted October 27, 1931, to which reference is made for amore detailed explanation of the operation ofthe motor synchronizing scheme.

Although a single frequency controlling line I2 has been shown for the polar relays -I'I, I8 and 20, it will be understood that, if desired, individual lines I2 may extend to each of the automatic transmitters, and such would be the case if the transmitters are separated from each other any appreciable distance. p

'I'he multiplex distributor I9 consists of any suitable means for assigning the various channels to the multiplex equipment 24. In the arrangement herein shown in the drawings merely for the sake of simplicity, the distributor comprises a plurality of segments 2|,.22 and 23, each segment being individual to a channel, and a brush assemblage 25 adapted to sweep over the segments and to obtain therefrom the signal units or pulses transmitted by the land channel equipment. The brush assemblage 25 which is connected to multiplex equipment 24, is arranged to make one revolution for each dot cycle of the automatic transmitter equipment, thisdot cycle comprising the basic unit. Actually, the distributor which is used is quite diierent as will appear later in the description. In the present instance, since a three channel circuit ls shown, the distributor is arranged to supply to the multiplex equipment at most one-third of a dot length of each unit of signal received from the respective channels alternately, thus throwing away the other two-thirds or more of the dot unit which is later restored by a rebuilding circuit in the receiver. which, infturn, actuates the radio transmitting equipment l, is assigned to the successive channels I, 2 and 3 and their respective land lines 4, 5 and 6 consecutively for a time equal to at most,one of these one-third dot portions. v

It will be apparent from Fig. 1 that although threechannels are shown, any number of channels may be used. For three channel working, clearly only one third of each signal component is actually operative for each channel, and similarly for larger numbers of channels. This manner of dividing the line time of the multiplex equipment into the various channels is described in great detail in United States Patent No. 1,979,484, supra, to which reference is made.

In actual practice, the distributor I9', which has been herein shown in its present form for the sake of simplicity, is quite diierent and consists of stationary brushes with a commutator bar forming a momentary short circuit between pairs of brushes. Such a distributor is fully described in Reissue Patent No. 192626, granted to R. E. Mathes, June25, 1935, and functions to select only fa small portion of the signal from the middle of the full dot length of each channel and to assign it to the locking circuit 24 described below, the locking circuit, in turn, elongating this small middle portion to one-third of the full dot length (if three channel working is employed). This small middle portion is equal to about onetenth to one-twentieth of a ,full' dot length.

The multiplex receiving equipment 24 with which the distributing brush-assemblage 25 is connected comprises essentially a locking circuit 26 and a tone keyer arrangement 28 for producing tone signals in transmission linea, Yextending to the ,antennal equipment l, whichV corresponds to the compositeV signal received from the .tube blocked,` or prevented from passing current.

The changefrom onecondition-of stable' equilibrium, such as when device 29 is blocking and device 30 is passing, to the other. condition when device 29 is' passing and device 39 blocking, or the reverse, is caused bythe lpresence of a suitable predetermined potential on the 'brush assemblage 25. That is to say, there exists a predetermined maximum anode kcu1rent. flow, in one `of the electron dischargev devices and a predetermined vminimum anode current fow in the other electron ,discharge device, or` the reverse, at-the throughonejoftl'ie devices 29 or 30, the energization of the antenna 'l through the intermediary of the apparatus 28 may readily be controlled.

The `rmultiplex equipment 24 transmitted to the central oilice.

This particular manner of controlling an antenna system by means of the multiplex equipment shown comprising a locking circuit 26and a tone keyer 2B, is adequately described in the literature relating to communication systems and, therefore, need not be further described herein. For a more amplified description of such manner of telegraph communication, however, reference is made to United States Patent No. 1,844,950, granted February 16, 1932, to J. L.

Finch.

Referring now to theremote trunk station of Fig. 2, the composite signals are received -over any suitable type of antenna system, amplied, and detected in a well known manner, and then It is preferred,

in the present'system, to use a diversity receiving antenna arrangement of the type which is described in United States Patent No. 1,874,866, granted August 30, 1932, to H. H. Beverage et al. In this particular arrangement the signals are received over a plurality of geographically separated antennae, amplied, detected and combined in a suitable device for operating a tone keyer which is arranged to transmit audible frequencies which are interrupted in accordance with the received signal. These audible interrupted frequencies are fed from the. antenna system into a landline 3l for transmission to the distant central oiiice at which vthey are defor enabling the received signals to be rebuilt to their-'original form as at the transmitting station whereby the vsuppressed portions of f the transmitted signals are restored. Distributor arrangement is driven by drive motor 36 which is held in synchronism with the multiplex distributor driving mechanisrnat'the transmitting 4station, Fig. 1, by means. of correction `unit'3`l, ythe latter in turn being controlled by the/incoming signal. Associated with the individual segments of distributor 35 are condensers 38, 39 land 4G and locking circuits 4I, 4.2 and 43 which are individual to the respective channels. v These locking ycircuits which 'are of the ytype described. in Finch United StatesPatent No. 1,844,950, supra, function to operate suitable utilization' means in theA output circuits lof the `channels and to reproduce'A the original signal characters transmitted whether they are of they Morse orprin'ter type. vThe particulanmanner in which the coupling device 34 and distributor 35 with the associatedlocking circuits; function to reproduce the transmitted signal is vdescribed :in United States Patent -No.

'1,995,181,.`gran`ted to Alfred Kahn, March'l19,

As hereinabove .mentioned in connectionkwith the transmitting distributor of Fig. l, the distributor, in practice, is somewhat diiferentfrom that illustrated andy consistsfof an arrangement such as is ydescribed in Reissue Patent No.,.19,626, supra. This distributor at the receiverselects onlya small portionof the signal of ea'ch channelv from the center of the individual one-third dot length and assigns it'to its proper receiving locking circuit which, in turn, elongates the portion to its full dot length.

For maintaining drive motor 36in synchronism,

5 there is employed any suitable type of synchronous correction circuit which is under control of the received signals. It is preferred to use a synchronous arrangement which is controlled by the steep slope or wave front of the rectified signal for operating a. correction motor. A system of this type is described in the said patent to R. E. Mathes, No. 2,038,375.

If desired, a monitoring circuit, such as 44, may be employed for observing the incoming composite signal after rectification, but before application to the coupling tube 34. This monitor circuit may employ acoupling system similar to device 34 shown inl the drawings.

For storing the received signals priorto retransmitting them to the remote branch oiiice stations, there are provided reperforators 44 which translate the signal impulses into characters on tape. If it is desired to relay the signals on only two channels, then there may be provided A any suitable utilization circuit, such as a printer trolled in a manner similar to that hereinbeforev described by a brush arrangement 41 located'on a multiple unit distributor motor shaft device.

' This control of the automatic tape transmitters is herein indicated schematically by dotted lines 48.

For transmitting the signals to the branch of- `4r) ce station, Fig. 3, the outputs of the automatic tape transmitters 46 arecoupled via the segments of one section of the multiple unit distributor device 49-52 to an antenna 50 which'is directed upon the branch omce station. The wiring arrangement of portion 43 of the multiple unit distributor 49, 52, its associated locking circuit and keyer 5l, and antenna 50, is similar to the wiring arrangement of distributor I9, locking circuit 24, keyer 28, and antenna l of Fig. l, pre- 50 viously described.

A portion of distributor..52 which is a part of multiple unit distributor 4352,is in circuit with a receiving arrangement comprising antenna. 53, receiver 54, detector and tone' keyer 55 and rectifier unit 56,.` These elements are connected together in the Ysarnemanner as similar parts of the receiving elements associated with distributor 35. Antenna 53 is directed t o receive signals sent out by a branch oie station as shown by Fig. 3. A transmitting arrangement comprising 75 stood that a signal originating in the remote a locking circuit 51, an amplier 58, and an antenna 59 obtain the signals collected by antenna 53, as the brush of distributor 52 sweeps over the segments and transmits backto the local trunk "station Fig. 1.` It should be understood the local trunkstation is equipped with a receiving arrangement as shown on Fig. 2, except thatthe reperforators or suitable storage apparatus are replaced by recording equipment.' From the foregoing lit will be understood, of course, that other receiving circuits similar to 53, 54 and 55 may be associated with the other segments of distributor 52 for receiving signals from other branch oilice stations like that of Fig. 3'. It will also be undersegments.

trunk oiiice or connected by wire line to it can be combined with the branch ofiice signals in distributor 52.

The operation of the system of Fig. 3 will be obvious from what has been said before. The signals transmitted from the remote trunk station of Fig. 2 are received on a circuit identical with those described hereinabove to receive signals at the remote trunk station. For transmitting signals from the branch ofiice station to the remote trunk station, however, there is provided an automatic tape transmitter 60 whose motor 6l is controlled from the shaft 62 of the motor 63. Since the speed of the distributor motor 63 is controlled by the steep wave front of the signals incoming from the remote trunk station, it will be seen that the signals outgoing from'the branch oce station are also synchronized.

In the operation of the system as a whole, Morse code signal characters are transmitted from automatic tape transmitters 9, i0, and il (Fig. 1) and are delivered to the multiplex transmitting system as brush assemblage 25 sweeps over the Only a portion of the basic unit comprising the dot length is obtained from each channel while the remaining portions of the dot Alength unit are discarded. Multiplex distributor I9 is driven at constant speed under control of motor drive unit I6, the latter in turn functioning to control the rotating mechanism at the distant automatic Morse code transmitting stations. In this manner all signals in the various channels remain under control of the multiplex distributor which assigns the multiplex equipment at predetermined intervals to each of the channels' successively for an interval equal to a predetermined .portion of the basic dot length unit. 'Ihe composite signal composed of positive and negative pulses, received by the multiplex equipment 24, is utilized to energize the radiating antenna equipment 1. At the remote trunk station the signals are picked up by a suitable energy collector, rectified, and the rectified portions of the composite signal-applied to a coupling system which, in combination with a distributor 35,

synchronously controlled by the incoming signals to rotate at a rate of speed the same as the distributor of the transmitting station, assigns portions of the received signal, which correspond with theportions obtained from the transmitting channel at the transmitting station, to the respective receiving channels where, through a suitablecondenser and locking circuit arrangement, as shown, spacing and marking pulses are generated similar to those originally transmitted to affect the respective reperforators which store the signals on tape.

A slight interval of time later the stored signals are retransmitted by automatic tape transmitters 46 under control of section 49 of multiple unit distributor 49-52, to the branch -oiice station, Fig. 3, where they are not only recorded but also utilized to synchronize the receiving and transmitting equipment thereat.

It will be understood that any number of branch stations, and various combinations of automatic tape transmitters may beemployed, as is desired; 'I'hese transmitters may be located as near or as far removed from each other and froml their associated stations as convenience and necessity dictate.

What is claimed is: 1. In a multiplex telegraph relaying syste comprising a local trunk station, a remote trunk station, and a branch oflice station, the method of local station a plurality of message signals corresponding to the number of channels in the system, dividing the successive basic time units of the message characters of each channel. into equal portions of like number as the total number of channels used' and transmitting a composite signal formed by combining equal portions from the successive channels consecutively and discarding the remaining portions cf the basic time units, receiving said composite signals at said remote trunk station, breaking down the composite signal into the different selected message portions, restoring the latter to have periods of time corresponding with those of the original message characters prior to division and selection -at the transmitter, storing the different message signals, transmitting from said remote trunk station to said branch ofilce station a composite signal similar tov that received by said remote trunk station, said composite signal being formed lof selected portions of the stored signals, and

receiving said composite signal at said branch oflice station.

2. A multiplex telegraph system having, in combination, a local trunk station and a remote trunk station, means in circuit with said local trunk station for producing a pluralityof message signals and separate means for dividing' the successive basic units of the characters of each message signal into equal portions of like number as the total number of channels used,

and for combining equal portions from the suc-- cessive channels consecutively into -a composite signal, and additional means in circuit Withsaid local station for transmitting said composite signal tosaid remote trunk station, means at said remote trunk station for receiving saio. composite signal and breaking same down into the different message portions and for restoring the latter to have periods of time corresponding with those of the original message characters prior to division, a vreperforator at said remote trunk station individual to each channel for recording the mes- -1 -into equal portions of like number as the total number of channels used, and for transmitting to said remote trunk station a composite signal formed by combining equal portions from the successive channels consecutively, means at said remote trunk station for receiving said composite signal and breaking same down into the different `message portions andior restoring -the latter to` have periods of time corresponding with those of the original message characters prior to division, a reperforator at said remote trunk station individual to each channel for recording the message signals of each channel on tape, an4

to produce a composite signal formed of equal portions selected from the tape. transmitters, means for transmitting said last compositey signal, and a distant branch oilice station for receiving said composite signal from said `remote trunk station.

4. A multiplex telegraph system having, in combination, a local trunk station and a remote trunk station, means in circuit with said local trunk station for producing a plurality of message signals and for dividing the successive basic units oi the characters of each message signal into' equal portions oflike number as the total number of channels used, and for' transmitting to said remote trunk station a composite signal formed by combining equal portions from the successive channels consecutively, means at saidl remote trunkstation for receiving said composite Asignal and breaking same down into the dify station individual to each channel for recording the message signals of each channel on tape, an automatic tape transmitter for each reperforator arranged to receive the tape from its associated reperforator for producing signal pulses corresponding to the characters on said tape, and means at said remote trunk station similar to that at said local trunk station for combining the signal pulses from said tape transmitters to produce a composite signal formed of equal portions selected from the'tape transmitters, means for transmitting said last composite signal, and

a distant branch oiiice station for receiving said composite signal from said remote trunk station, rotating mechanism and an automatic transmitter at said distant branch omce station, the speed of said transmitter being under vcontrol of said rotating mechanism, the phase and speed of said rotating mechanism being under control of the composite signal received from said' remote trunk station.

5. In atelegraph relaying system, the method of maintaining synchronism among a group of stations, each of which has rotating mechanism thereat which comprises transmitting message signals from one station to another, utilizing said message signals to control the speed and phase of the mechanism at said last station, storing said signals, relaying said signals to still another station, and utilizing said relayed signals to control the speed and phase of said last station wherebythe rotating machinery at all of said stations arecontrolled in a predetermined manner.

6. In a radio telegraph relay system, a remote trunk station having a single unit distributor and a motor therefor, and a multiple unit distributor and a motor therefor, signal receiving apparatus associated with the said single unit distributor for receiving signals from a distant trunk station, signal transmitting apparatus and additional receiving apparatus in circuit with said multiple unit distributor, means in circuit'with said single unit distributor for storing signals received over said first receiving apparatus and for subsequently sending out corresponding signals over said transmitting apparatus through one unit of said multiple unit distributor to a branch station or stations, said branch station remote trunk station signals which arer controlled' as to speed.

7. In a telegraph relaying system, the method 5 of maintaining synchronism among a. group of stations, each of which has rotating mechanism `thmeai'. which comprises transmitting message signals from one station to another, utilizing said message signals to control the speed and lo phase of the mechanism at said last station, storing said signals and subsequently relaying said stored signals to still another station, and utilizing said relayed signals to control the speed and phase of said last station whereby the rol5 tating machinery at all of said stations are controlled in a predetermined manner.

8. 1n a telegraph relay system, a relay station having a single unit distributor and a multiple unit distributor, separate motors` for driving each 20 of said distributors, signal receiving apparatus associated with said single unit distributor for receiving signals from a distant transmitting station, means at said relay station controlled by acecr the receivedsignais from said distant transmitting station for controlling the speed and phase of the motor driving said single unit distributor, additional apparatus comprising rst and second signal transmitting equipment and additional receiving equipment in circuit with said multiple unit distributor, said second signal transmitting equipment and said additional receiving equipment being connected to one unit and said rst transmitting equipment to another unit of said multiple unit distributor, means including signal storage apparatus in circuit with said single unit distributor for storing signals received over its associated receiving apparatus and subsequently sending out corresponding signals over said ilrst transmitting apparatus through said multiple unit distributor to a distant terminal station, said additional receiving equipment being adapted to receive signals from said distant terminal 

